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Guest Column

The link between eating meat and cancer

By DR. V. UPENDER RAO
Published December 11, 2006

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Dietary factors have been implicated as having a causal role in several cancers including gastrointestinal, breast, prostate, stomach and esophagus. However, there is no strong evidence in the medical literature for such a role.

A large study, the European Prospective Investigation into Cancer and Nutrition cohort, examining the causal role of meat consumption in esophageal and gastric cancers, was conducted across 10 European nations. The study accrued 521,475 men and women, ages 35 to 70, and examined their dietary and lifestyle habits. The mean follow up of participants was 6.5 years.

Within this large study was a nested case control study that evaluated the combined role of Helicobacter Pylori infection and meat consumption in esophageal and gastric cancers.

The results of this study showed:

-There was a statistically significant risk for noncardia gastric cancer associated with consumption of all meat, red meat and processed meat. The cardia is a part of the stomach. Cancer arising there is cardia adenocarcinima; noncardia adenocarcinomas are cancers arising in the rest of the stomach.

-The risk for noncardia gastric cancer was particularly high for meat consumers who also had Helicobacter Pylori infection. The infection could be current or previous with persistent antibodies to H. Pylori.

-A positive but statistically nonsignificant association was found between meat consumption and esophageal adenocarcinoma only in the calibrated model.

-There was no association between meat consumption and cardia gastric cancer.

The carcinogenic mechanisms involved in red meat consumption and H. Pylori infections are not fully elucidated. Red meat is a dietary source of iron, which is thought to be an important growth factor for H. Pylori. Paradoxically, however, although the consumption of red meat is increasing in most western countries, the incidence of H. Pylori infection and that of noncardia gastric cancer is on the decline.

Other contributing factors may involve fat, protein, nitrite, nitrosamines, heterocyclic amines, polycyclic aromatic hydrocarbons, and salt. All of these compounds are either associated with the method of cooking, preparation and or preservation of meat.

The formation of some of these offending compounds seems to be related more directly to iron rather than protein. Salt is thought to damage the protective layer of the stomach by inducing inflammation. Although sodium nitrate contents had decreased in the past 20 years, it is still widely used as a preservative in cured meats.

Other contributing factors are the method of cooking. High temperature cooking and cooking over an open flame produce some of the carcinogens previously mentioned.

Since the cellular and sub cellular mechanisms of gastric and esophageal cancers are still not fully understood, it is difficult to make any recommendations. One could make a case for avoiding and promptly treating all H. Pylori-infected patients, including those who are asymptomatic.

While H. Pylori may have a causal role in gastric cancer, it is thought to be protective against adenocarcinoma of the esophagus. Moreover, whereas the incidence of gastric cancer is on the decline, that of adenocarcinoma of the esophagus is actually on the increase. The eradication of all H. Pylori infections may therefore be counter productive because of the removal of a layer of protective mechanism against adenocarcinoma of the esophagus, whose incidence is actually rising.

Avoiding cured and preserved meats and high-salt diets may be protective both from a cancer and cardiovascular perspective. The inclusion of fruits and vegetables and regular exercise - and the elimination of cigarette smoking, obesity and excess alcohol consumption - will all help.

The EPIC study was reported in the March issue of the Journal of the National Cancer Institute. This is the largest cohort study examining the association of fresh and processed meat and gastric cardia and noncardia adenocasrcinoma. It is the first study evaluating the association of meat and adenocarcinoma of the esophagus. It is also the first cohort study reporting the role played by H. Pylori in gastric cancer.